Mycobacterium avium (MAC) Flashcards
Define MAC
Mycobacterium avium (MAC) refers to infections caused by one of two nontuberculous mycobacterial species, either M. avium or M. intracellulare
Etiology of MAC in HIV infected populations vs. immunocompetent patients
- Infection with these organisms can occur in patients with or without HIV infection
- The two principal forms of MAC infection in patients with HIV are disseminated disease and focal lymphadenitits
- By contrast, isolated pulmonary infection is typically seen in immunocompetent patients
What has caused decline of deaths d/t MAC in HIV patients?
Dramatic declines in the rate of new MAC cases is seen with the use of prophylaxis early in the epidemic, and more recently, the widespread use of effective HAART
MAC mode of infection
- Mode of infection is through respiratory (inhalation) and GI tract (ingestion) with bacteremia following dissemination via the lymphatics
- MAC organisms are ubiquitous in the environment, including water and soil
- Person-to-person or common source of transmission appears to be rare therefore there is no need for isolation of hospitalized patients
How does MAC infection occur?
- Thought to result from recent acquisition rather than reactivation, since latent infection does not exist with this organism
- Among HIV-infected patient, MAC infection is MC seen among those with CD4 count < 50 cells/microL
MAC - disseminated disease etiology and symptoms
- Common presentation prior to widespread use of ART
- Symptoms are nonspecific and include: fever, night sweats, abdominal pain, diarrhea, weight loss and cough
- Lymphadenopathy can occur but more likely to be diffuse and less noticeable than in localized disease
Lab abnormalities in disseminated MAC
- Anemia
- Elevated ALP
- Lactate dehydrogenase
Diagnosis of disseminated MAC
- Made by isolation of the organism in culture, usually of the blood, lymph node or bone marrow
- Blood cultures are the preferred initial test as they are less invasive
- CT imaging may be helpful but can be relatively insensitive (findings can include lymphadenopathy, hepatosplenomegaly and/or small bowel thickening)
Symptoms of focal lymphadenitis
- Fever
- Leukocytosis
- Focal inflammation in a lymph node (e.g., cervical, intraabdominal, mediastinal)
How does MAC focal lymphadenitis occur in HIV patients?
In patients with HIV infection, most cases of MAC lymphadenitis result from an immune reconstitution inflammatory syndrome (IRIS)
- Develops about 4 weeks after ART is initiated**
- Can present due to IRIS in patients without a prior diagnosis of MAC
- Can develop in those with previously diagnosed disseminated infection
Explain IRIS
The immune system begins to recover, but then responds to a previously acquired OI secondary to an overwhelming immune mediated inflammatory response making the symptoms of infection worse
ART and focal lymphadenopathy
ART should be continued and (even though symptoms related to IRIS may last for weeks) most patients are treated successfully with antimicrobial therapy alone
Which antimicrobial agents have activity against MAC?
- Agents with activity against MAC include clarithromycin, azithromycin, ethambutol, rifabutin, amikacin, streptomycin and fluoroquinolones
- Treatment with more than one agent is necessary to decrease risk of drug resistance
*For most patients she initiated a dual therapy with a macrolide (azithromycin or clarithromycin) plus ethambutol
Prevention of MAC disease
- If CD4 count falls to < 50 cells/microL, MAC prophylaxis should be started in a patient with previous MAC infection and treatment for it
- When prophylaxis is indicated: weekly azithromycin (1200mg once weekly) or daily clarithromycin (500 mg twice daily)
- -Rifabutin is an alternative; however if used, active TB should be ruled out first
